> The initial default encoding for documents is the same as
> the Windows system code page (GetACP()). As user chooses an
> encoding from the View.Encoding menu, it becomes the new
> default.

My own experimentation with IE5 indicates that it only becomes the new
default if the user has Auto-Select (in the View > Encoding menu) off. When
Auto-Select is on, the default (and thus, document.defaultCharset) cannot be
changed.

Regardless of the Auto-Select setting, user selections do change how the
current document is interpreted (and thus, document.charset is modified).